Selective ion sensitive electrode and method of making it

ABSTRACT

A selective ion sensitive electrode is so constructed that an ion exchanger sensitive to a specific ion is formed on a metal electrode, an electric conductive resin electrode or a chlorinated metal electrode to which a signal wire is connected so as to maintain a stable electric connection between the signal wire and the ion exchanger over a long period of time. A layer of a silane coupling agent is used between the electrode member and ion exchanger.

BACKGROUND OF THE INVENTION

The invention relates to a selective ion sensitive electrode, and moreparticularly, to such electrode which may be used to determine theconcentration of a specific ion contained in a solution to be examined.

There have been proposed various selective ion sensitive electrodeshaving an ion sensitive assembly which is selectively sensitive to aspecific ion for determining the concentration of the specific ion bycomparing a potential developed across an interface between a solutionto be examined and the ion sensitive assembly when the latter isimmersed into the former with a suitable reference potential. FIG. 1illustrates an example of conventional selective ion sensitiveelectrodes. Such electrode is so constructed that a supporter 3 holdingan ion exchanger 2 which is selectively sensitive to a specific ion isjoined to one end of a stem 1 made from material such as glass,polyvinyl chloride or the like with adhesives 4 such as silicon RTVrubber manufactured by SHINETSU Chemical Co., Ltd. A signal wire 5formed with coaxial cable has its one end connected to the supporter 3by passing through the stem 1 and through the medium of an electricconductive resin 6. In the selective ion sensitive electrode thusformed, when the side of ion exchanger 2 which acts as an ion sensitiveassembly is immersed into a solution to be examined an interfacepotential corresponding to the concentration of a specific ion may bedeveloped across an interface between the ion exchanger 2 and thesolution to be examined, thereby enabling a determination of theconcentration of the specific ion to be made by detecting the interfacepotential.

However, because such a conventional selective ion sensitive electrodeis formed so that the signal wire 5 is connected to supporter 3 or ionexchanger 2 through conductive resin 6, there are disadvantages in thatits manufacturing is difficult, the joining strength between signal wire5 and supporter 3 is small and a mechanical failure often occurs.Therefore an inconvenience is experienced in that stable use over a longterm of time can not be expected.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a selective ion sensitiveelectrode in which an ion exchanger selectively sensitive to a specificion is formed on a metal electrode member, an electrically conductiveresin electrode or a chlorinated metal electrode to which a signal wireis connected.

In accordance with the invention, an ion exchanger is formed on a metalelectrode member or the like. Easy manufacturing of the selective ionsensitive electrode and stable performance of an electric connectionbetween the signal wire and the ion exchanger over a long period of timeare achievable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section illustrating an example of conventionalselective ion sensitive electrodes.

FIG. 2 is a cross section of a selective ion sensitive electrodeaccording to an embodiment of the invention.

FIG. 3 is a cross section of a selective ion sensitive electrodeaccording to another embodiment of the invention.

FIG. 4 is a cross section of a selective ion sensitive electrodeaccording to a further embodiment of the invention.

FIG. 5 is a cross section of a selective ion sensitive electrodeaccording to a still further embodiment of the invention.

FIGS. 6(A) and (B) are an outside perspective view and a half cutawayperspective view of a selective ion sensitive electrode according to astill further embodiment of the invention.

FIG. 7 is a cross section of a selective ion sensitive electrodeaccording to a still further embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 2, in which a selective ion sensitive electrodeaccording to an embodiment of the invention is illustrated, theelectrode has a disc-shaped metal electrode 12 fitted into one end of astem 11 made from polyvinyl chloride. An ion exchanger 14 is formed soas to be substantially flush with the end plane of stem 11. This isachieved by applying or pouring a solution in which is dissolved anion-exchange substance or the like which substance is selectivelysensitive to a specific ion. This substance is dissolved in a volatilesolvent which is applied to metal electrode member 12 over a layer ofsilane coupling agent 13. The solvent is then permitted to evaporate.Subsequently a signal wire 15 formed as part of a coaxial cable isdirectly connected to metal electrode member 12 (upper surface in thedrawing) through stem 11.

The silane coupling agent 13, as is indicated by its molecular formulaR'Si(OR)₃, includes more than one reaction radical (methoxy, silanolradical or the like) strongly joinable by chemically bonding aninorganic substance (glass, metal or the like) into a portion of itsmolecular formula and another reaction radical (vinyl, epoxy, methacryl,amino radical or the like) which chemically bonds with an organicsubstance (all kinds of synthetic resins). Consequently the silanecoupling agent 13 acts as a mediator between inorganic and organicsubstances.

The effect of the silane coupling agent 13 differs depending upon aresin or an elastomer to be applied. By way of example, as to the silanecoupling agent, NUC Silicones, manufactured by Japan Uniker Co., Ltd.,A-186 [beta-(3,4 Epoxycyclohexyl)ethyltrimethoxysilane], A-187(gamma-Glycidoxypropyltrimethoxysilane), and A-189(gamma-Mercaptopropyltrimethoxysilane) are effective for polyvinylchloride and in addition A-189, A-1100(gamma-Aminopropyltrimethoxysilane) and A-1120 [N-beta-(aminoethyl)gamma-aminopropyl-trimethoxysilane] are suitable to nitrile.

On the other hand, in the selective ion sensitive electrode of theembodiment of the invention, the above-mentioned solution which formsion exchanger 14, utilizes a blend of, for example tetrahydrofuran(THF), a supporting substance such as polyvinyl chloride (PVC) ordioctyl adipic acid (DOA) and an ion-exchange substance sensitive to aspecific ion. When such solution is poured onto metal electrode member12, THF, which is volatile, evaporates, whereby substances other thanTHF remain on the surface of metal electrode 12. Of the remainingsubstances, PVC may be chemically bonded with metal electrode member 12by action of the silane coupling agent 13 as stated above. In addition,when a solution containing an ion-exchange substance is poured intopolyvinyl chloride stem 11, a part of the inner wall thereof dissolves,thereby the stem 11 is bonded with the ion-exchanger 14 by merging ofPVC supporting the ion-exchange substance after evaporation of the THF.

When the selective ion sensitive electrode of the embodiment thus formedis immersed in a solution to be examined, a potential corresponding tothe concentration of a specific ion, as is the case with a conventionalselective ion sensitive electrode illustrated in FIG. 1, may bedeveloped across an interface between ion exchanger 14 and the solutionto be examined, therefore permitting a determination of the specific ionconcentration in the solution.

According to the electrode of the embodiment, the ion exchanger 14 isbonded with the PVC of stem 11 by action of THF in the solution and alsois chemically bonded with the metal electrode member 12 by action of thesilane coupling agent 13. Consequently a lowering of life of theelectrode due to permeation of a solution to be examined between thestem 11 and the ion exchanger 14 can be avoided.

Furthermore, the signal wire 15 is directly connected to the metalelectrode member 12, and not through a conductive resin, thus enablingthe connection to be firm. As a result, it will be noted that with metalelectrode member 12 and stem 11 firmly secured to ion exchanger 14, aselective ion sensitive electrode having a durable and compactconstruction and easy handling can be obtained.

In addition, compared with a conventional electrode, the one of theabove embodiment has a smaller number of parts and therefore it iseasier to manufacture. Thus these electrodes which are inexpensive andhave uniform performance may be mass produced.

Still further, it should be understood that since ion exchanger 14 canbe securely held on metal electrode member 12 its surface area can beincreased. Thus a quick responding electrode is obtainable.

FIG. 3 illustrates a selective ion sensitive electrode of anotherembodiment according to the invention. The electrode has an electrodemember 16 upon which is formed an ion exchanger 14. Member 16 is madefrom a thermoset conductive resin or a metal chloride. The electrodemember 16 thus formed is fitted into one end of stem 11, electrodemember 16 being held in an inner stem 17 made from glass or the samepolyvinyl chloride as stem 11. This is a departure from the electrodeshown in FIG. 2. Other members of the embodiment are constructedsimilarly to those of an electrode in FIG. 2. Accordingly, correspondingparts are designated by like reference numerals or characters withoutrepeating their description. It is also to be noted that metal chloridesare generally easily obtainable by means of an electrochemical techniqueusing a diluted hydrochloric acid solution.

It should be also understood that with the electrode of the embodimentthus formed the same function and effect as indicated in that shown inFIG. 2 can be obtained.

FIG. 4 illustrates a selective ion sensitive electrode of a furtherembodiment of the invention. The electrode, in which a coaxial cable isnot used as a signal wire, has a signal wire 19 integral with a metalelectrode 18 by machining the metal electrode 18 associated with ionexchanger 14. The whole member thus formed except a portion of ionexchanger 14 in contact with a solution to be examined is covered withan insulating member 20. A metal stem 21 is disposed around the outerperiphery of insulating member 20 so as to provide a shielding effectand another insulating member 22 is disposed around the outer peripheryof metal stem 21 except a portion in engagement with an electrode holder(not shown in the drawing). In this case the ion exchanger 14, which issimilar to the electrode shown in FIG. 2, is formed on a metal electrode18 over the silane coupling agent 13.

The selective ion sensitive electrode of the embodiment has a functionand an effect similar to that shown in FIG. 2. Since signal wire 19 andmetal stem 21 of the electrode may also serve as a connector (comparedto a conventional electrode which incorporates a BNC connector), itsmanufacturing cost can be advantageously decreased. Consequently, it isalso noted that when the electrode has not carried out its function, itis interchangeable without changing a connector and also can be easilyinterchanged when the concentration of a different ion is to bedetermined.

FIG. 5 illustrates a selective ion sensitive electrode of a stillfurther embodiment of the invention. The electrode includes a conductivethin film 23 of 0.1 to 5μ thickness formed of corrosion resistant Au,Ag, Pt or an alloy thereof on the under and side surfaces (see FIG. 5)of metal electrode member 12 by an electrochemical technique,sputtering, CVD (Chemical Vapor Deposition) method, vacuum evaporationmethod or the like. An ion exchanger 14 is formed on the under surfaceof metal electrode member 12 which the conductive thin film 23 covers,over the layer of silane coupling agent 13. A signal wire 15 formed witha coaxial cable is directly connected to the upper surface of metalelectrode member 12 within stem 11.

A corrosion resistant conductive thin film 23 is formed on metalelectrode member 12 to solve the problem of limited life when a basemetal such as Cu, Fe, Ni or the like or an alloy such as brass or thelike is used to form metal electrode member 12. However, when a noblemetal such as Au, Ag, Pt or the like having a good corrosion resistanceis used for the entire electrode 12 cost is increased. Accordingly, inthe electrode of the embodiment, a corrosion resistant conductive thinfilm 23 is formed on at least one surface of metal electrode member 12,in particular on at least the surface on which ion exchanger 14 isformed. An electrode member 12 can be formed with a high conductivityand low cost material such as Cu or the like and even when the thin film23 is formed with a noble metal such as Au, Ag, Pt or the like the filmthickness can be extremely small, therefore producing an inexpensive anddurable electrode.

FIGS. 6(A) and (B) illustrate a selective ion sensitive electrode of astill further embodiment of the invention. In this electrode, which is athrough-flow type, a rectangular opening is formed on a part of a hollowinsulating stem 31 through which a solution to be examined flows and anelectrode assembly 32 is disposed over the opening so as to determinethe concentration of a specific ion contained in the solution to beexamined while the solution flows through the stem 31. The electrodeassembly 32 is formed with a conductive thin film 34 of 0.1 to 5μthickness made from a noble metal such as Au, Ag, Pt or the like on theinside of a saddle-shaped metal electrode 33 and an ion exchanger 36 isformed on the film 34 over a layer of silane coupling agent 35. Theelectrode assembly 32 is secured to the area of stem 31 around theopening with insulating adhesives such as epoxy resin or the like and asignal wire 37 is connected to the outer surface of metal electrode 33.

The electrode assembly 32, which is provided at a portion of hollowinsulating stem 31, may be provided around the periphery thereof.Specifically a ring-shaped electrode is employed as metal electrode 33and an ion exchanger 36 may be formed over a conductive thin film 34 andthe layer of silane coupling agent 35 on the inner periphery of theelectrode.

In the electrode of the above embodiment which is formed as athrough-flow type, the same function and effect as indicated for theelectrode shown in FIG. 5 are obtainable.

FIG. 7 illustrates a selective ion sensitive electrode of a stillfurther embodiment of the invention. This electrode differs from the oneshown in FIG. 5 only in that a surface of metal electrode member 12A onwhich an ion exchanger 14 is formed is made rough to the extent that theroughness is 1 to 100μ and a conductive thin film 23 is formed on therough surface. It will be understood that when the surface of metalelectrode members 12A on which thin film 23 is formed is made rough theadhesion between thin film 23 and ion exchanger 14 can be improved. Itshould be also understood that in the electrode of a through-flow typeshown in FIGS. 6(A) and (B), if the inner surface of metal electrode 33is made rough to the extent that the roughness is 1 to 100μ the adhesionbetween ion exchanger 36 and thin film 34 can be improved.

In each of the above-mentioned embodiments, while a metal electrodemember includes an ion exchanger which is formed over a layer of silanecoupling agent, if the adhesion between the metal electrode and the ionexchanger is strong the silane coupling agent may be dispensed with.

It is also to be noted that in the electrode of the embodiments of FIGS.5 to 7, while a conductive thin film is formed on a surface of the metalelectrode member on which an ion exchanger is formed, it may be formedso as to cover the whole surface of the metal electrode member.

What is claimed is:
 1. A selective ion sensitive electrode including anion exchanger selectively sensitive to a specific ion, comprising:anelectrode member to which a signal wire is connected on one sidethereof, said member comprised of one of a metal, an electricallyconductive resin and a chlorinated metal; a corrosion resistantconductive thin film formed on the opposite side of said electrodemember from said signal wire; a layer of a silane coupling agent on saidcorrosion resistant conductive thin film; and an ion exchanger formed onthe surface of said layer of a silane coupling agent.
 2. A selective ionsensitive electrode according to claim 1 in which the ion exchanger isformed by the process comprising the steps of applying a solutionincluding at least an ion-exchanger substance, dissolved in a volatilesolvent onto the layer of a silane coupling agent and allowing thesolvent to evaporate.
 3. A selective ion sensitive electrode accordingto claim 2 in which the solution further comprises a supportingsubstance selected from the group consisting of polyvinyl chloride anddioctyladipic acid.
 4. A selective ion sensitive electrode according toclaim 1 further comprising a stem in which the electrode member is held,the stem comprising a substance which is in part merged into the ionexchanger.
 5. A selective ion sensitive electrode according to claim 1in which the electrode member is comprised of a metal and the signalwire is integrally formed with the metal electrode member.
 6. Aselective ion sensitive electrode according to claim 5, furthercomprising an insulating member surrounding the signal wire and a metalstem surrounding the insulating member, the metal stem serving to shieldthe signal wire.
 7. A selective ion sensitive electrode according toclaim 1 in which the electrode member is a metal.
 8. A selective ionsensitive electrode according to claim 7 in which the corrosionresistant conductive thin film is made from a noble metal.
 9. Aselective ion sensitive electrode according to claim 7 in which the ionexchanger is formed by the process comprising the steps of applying asolution including at least an ion exchange substance dissolved in avolatile solvent onto the conductive thin film and allowing the solventto evaporate.
 10. A selective ion sensitive electrode according to claim7 in which the surface of the metal electrode member on which the ionexchanger is formed is made rough with a roughness of 1 to 100μ.
 11. Aselective ion sensitive electrode according to claim 8 in which thenoble metal is selected from the group consisting of gold, silver andplatinum.
 12. A selective ion sensitive electrode according to claim 10further comprising a stem in which the electrode member is held, thestem comprising a substance which is in part merged into the ionexchanger.
 13. A selective ion sensitive electrode according to claim 1in which the signal wire is connected directly to the electrode member.14. A sensitive ion selective electrode according to claim 13 in whichthe electrode member is comprised of a metal and the signal member isintegrally formed with the metal electrode member.
 15. A selective ionsensitive electrode according to claim 1, further comprising a housingfor supporting said electrode member, said housing being formed from anonconductive material, said electrode member being contained within anopening within said housing so that said ion exchanger is flush with asurface of said housing.
 16. A selective ion sensitive electrodeaccording to claim 15, further comprising an inner housing member forholding said electrode member, said inner housing member being receivedwithin said opening.
 17. A selective ion sensitive electrode accordingto claim 16 in which the corrosion resistant conductive thin film ismade from a noble metal.
 18. A selective ion sensitive electrodeaccording to claim 15 in which said housing is formed as a cylindricaltube adapted to receive a liquid therein, said tube having an innercylindrical surface, an outer cylindrical surface and an opening in saidtube between said inner and outer surfaces, said electrode member beingformed to conform to said outer surface adjacent said opening and tocover said opening, said ion exchanger being flush with said innersurface.
 19. A selective ion sensitive electrode according to claim 18in which the electrode member is ring-shaped and extends around theperiphery of the cylindrical tube.
 20. A selective ion sensitiveelectrode according to claim 19 in which the corrosion resistantconductive thin film is made of a noble metal selected from the groupconsisting of gold, silver and platinum.
 21. A selective ion sensitiveelectrode according to claim 18 in which the surface of the electrodemember on which the ion exchanger is formed is made rough with aroughness of 1 to 100μ.
 22. A selective ion sensitive electrodeaccording to claim 15 in which the electrode member is a metal.
 23. Aprocess of forming a selective ion sensitive electrode comprising thesteps of providing an electrode member to which a single wire isconnected on one side thereof, said member comprised of one of a metal,an electrically conductive resin and a chlorinated metal, a corrosionresistant conductive thin film formed on the opposite side of saidmember from said signal wire and a layer of a silane coupling agent onthe surface of said corrosion resistant conductive thin film; applying asolution having an ion exchange substance dissolved in a volatilesolvent to the surface of said layer of silane coupling agent; andallowing the solvent to evaporate to form an ion exchanger on said layerof silane coupling agent.
 24. The process of claim 23, furthercomprising the step of inserting the electrode member into an opening ina stem in which the electrode member is held before applying thesolution.
 25. The process of claim 24 in which the electrode member isinserted to a depth in the opening so that the ion exchanger formed isflush with a surface of the stem.
 26. The process of either of claims 24or 25 in which the portion of the stem is partly merged into the ionexchanger due to the action of the solvent upon the stem.